Potassium ion-specific membrane

ABSTRACT

A potassium ion-specific membrane includes a hydrophobic elastomeric polymer with a dielectric constant of from 4 to 13, and a potassium ion-specific carrier. The hydrophobic elastomeric polymer is preferably an organopolysiloxane polycarbonate block copolymer. The potassium ion-specific carrier is selected from the group consisting of nonactin, gramicidins, valinomycin, and mixtures thereof.

nited States Patent [1 1 rown, Jr. et a1.

POTASSIUM ION-SPECIFIC MEMBRANE Inventors: John F. Brown, Jr.; Oliver H.

LeBlane, Jr.; Willard T. Grubb, all of Schenectady, NY.

Assignee: General Electric Company,

Schenectady, NY.

Filed: Oct. 18, 1971 App]. No.: 190,197

US. Cl. 204/195 M, 204/296, 260/824 Int. Cl. G01n 27/30 Field of Search204/195 M, 1 T, 296;

References Cited UNITED STATES PATENTS 2/1971 Simon 204/195 M 12/1968Vaughn 260/824 R 9/1956 Patnode et al.. 204/195 M 2/1969 Ross 204/1 T 1Oct. 23, 1973 FOREIGN PATENTS OR APPLICATIONS 5/1965 France 204/195 MOTHER PUBLICATIONS G. A. Rechnitz, C & EN, pp. 146-158, June 12, 1967.

A. Durst, Ion-Selective Electrodes, pp. 89-94,

Primary ExaminerG. L. Kaplan Att0rneyFrank L. Neuhauser et a1.

ABSTRACT A potassium ion-specific membrane includes a hydrophobicelastomeric polymer with a dielectric constant of from 4 to 13, and apotassium ion-specific carrier. The hydrophobic elastomeric polymer ispreferably an organopolysiloxane polycarbonate block copolymer. Thepotassium ion-specific carrier is selected from the group consisting ofnonactin, gramicidins, valinomycin, and mixtures thereof.

2 Claims, 1 Drawing Figure PATENIEI] UN 23 I915 THE IR ATTORNEYPOTASSIUM ION-SPECIFIC MEMBRANE Reference is made to copending patentapplication entitled Ion-Specific Membrane filed Oct. 18, 1971, andgiven Ser. No. 190,344, which describes and claims an ion-specificmembrane comprising a hydrophobic elastomeric polymer with a dielectricconstant of from 4 to 13, and an ion-specific carrier.

This invention relates to potassium ion-specific membranes and, moreparticularly, to such ion-specific sensing membranes comprising ahydrophobic elastomeric polymer and a potassium ion-specific carrier.

Such ion-specific membranes are employed to measure specific potassiumion responses. These membranes can be used in various types of sensors.

Ion-specific sensors are known in the prior art for measuring thepotassium ion activity of a sample. For example, reference is made toUS. Pat. No. 3,562,129 issued Feb. 9, 1971, entitled Cation-SpecificElectrode System. This patent describes a membrane with an inertmaterial and a cation specific component. The inert material isimpregnated with a solution of the cation specific component which isselected from the group consisting of nonactin and its homologues,gramicidin and valinomycin. The membrane can consist of a porous,inactive material, for example, a glass frit, a filter paper or a wovennylon fabric, in which the active component is embedded. Polyethyleneand gel formers are also listed as examples. In column 4, lines 18-23,there is described a hot solution of a gel former in a suitable solvent,which is saturated with the cation specific component, and coated on toone side of the polyethylene foil.

Our present invention is directed to an improved potassium ion-specificmembrane wherein a hydrophobic elastomeric polymer with a dielectricconstant of from 4 to 13, and a potassium ion-specific carrier are mixedtogether in suitable manner such as in a solution of methylene chlorideand cast into a film on a glass plate from the solution.

Organopolysiloxane polycarbonate block copolymers, which are preferredin our present invention as hydrophobic elastomeric polymers, aredescribed and claimed in US. Pat. No. 3,419,634 issued Dec. 31, 1968 andassigned to the same assignee as the present application.

Our present invention is directed to an improved potassium ion-specificmembrane which is suitable for biomedical, environmental control andother applications.

In accordance with one aspect of our invention, a potassium ion-specificmembrane has a mixture of a hydrophobic elastomeric polymer with adielectric constant of from 4 to 13, and a potassium ion-specificcarrier.

These and various other objects, features and advantages of theinvention will be better understood from the following description takenin connection with the accompanying drawing in which:

The single FIGURE is a sectional view of a potassium ion-specificelectrode employing a potassium ionselective membrane made in accordancewith our invention.

In the single FIGURE of the drawing there is shown generally at apotassium ion-specific electrode employing a potassium ion-specificmembrane made in accordance with our invention. A tube 11 ofnon-ionselective material, such as glass has a disc 12 of potassiumion-specific membrane sealed to one open end of glass tube 1 1 by a roomtemperature sealant 13 holding the edges of disc 12 against the exteriorsurface of tube 11. A silver wire 14 is positioned partially within tube11 and extends outwardly from tube 11. Silver wire 14 has a portion ofsilver wire 15 and a portion 16 with silver chloride thereon. Tube 11 isfilled with a buffered saline solution.

We found that we could form an improved potassium ion-specific membrane,which is useful for sensing potassium ions, from a hydrophobicelastomeric polymer with a dielectric constant of from.4 to 13, and apotassium ion-specific carrier. Suitable hydrophobic elastomericpolymers with a dielectric constant of from 4 to 13 includepolyurethanes, chloroprene polymers, vinylidene fluoridehexafluoropropylene polymers, and organopolysiloxane polycarbonate blockcopolymers with a dielectric constant of from 4 to 13. Such blockcopolymers are described and claimed in the aboveidentified U.S. Pat.No. 3,419,634. For example suitable block copolymers with a dielectricconstant of from 4 to 13 include phenoxysilicon linked cyanoethylmethylsiloxane/bisphenol-A copolymer, siloxanecarbamate/BPA-carbonatecopolymer with diisocyanatosiloxane, siloxane-carbamate/BPA- carbonatecopolymer with a ratio of SiMe SiMeEtCN=3.3,siloxane-carbamate/BPA-carbonate copolymer with a ratio of SiMe/SiMeEtCN=2,4, siloxane-carbamate/BPA-carbonate copolymer with a ratioof SiMe /SiMeEtCN=0.l3, and siloxane-carbamate/B- PA-carbonate copolymerwith a ratio of SiMe SiMe(EtCN)=13.

The potassium ion-specific carrier is selected from the group ofnonactin, gramicidins, valinomycin, and mixtures thereof. Such carriersare known and described, for example, in the above-identified US. Pat.No. 3,562,129. The carriers may be employed in the form of the simpleacid or in various admixtures with hydrophobic, lipophilic salts of theacid such as tetraheptyl ammonium salts. Alternatively, the salt formingion may be structurally incorporated into the polymer to completelyprevent its transfer to the aqueous phase. Alternatively neutralhydrophobic, lipophilic salts such as tetraphenyl ammonium-tetraphenylborate may be added to the polymer. One of the purposes of adding thesalt forming species is to increase the conductivity of the membrane andthereby reduce interferences from electrical noise.

The following preparations are suitable to produce organopolysiloxanepolycarbonate block copolymers for use in preparing the membranes of ourinvention. 1. Phenox-ysilicon Linked Cyanoethyl-methylSiloxane/Bisphenol-A Copolymer A rnixture of 15.7 g ofpentamethylcyanoethylcyclotrisiloxane mmoles) and 1.3 g ofdimethyldichlorosilane (10 mmoles) and 20 mg of ferric trichloridehexahydrate was stirred overnight under anhydrous conditions. Anexothermic reaction was observed during the first minutes, accompaniedby a strong viscosity increase; the viscosity dropped during laterstages of the reaction. The resulting a, w-dichloropolysiloxane wasdiluted with 10 cc of anhydrous methylene chloride and added dropwisewith stirring under anhydrous conditions to a solution of 6.85 g ofbisphenol-A (30 mmoles) and 7.8 cc of dry pyridine in 60 cc of methylenechloride. The mixture was stirred for about 30 minutes after completionof the addition;

sic viscosity: 1; 0.59 dl/g.

2. Siloxane-carbamate/BPA-carbonate copolymer with diisocyanatosiloxaneA mixture of 44.5 g of octamethylcyclotetrasiloxane,

22.5 g of cyanoethylmethylcyclosiloxane (mixture of trito hexasiloxane)and 5.4 g of 1,3-bis (4- aminobutyl)tetramethyldisiloxane was heatedwith about 20 mg of solid sodium hydroxide under dry nitrogen at 170overnight. A solution of 14 g of the resulting homogeneous fluid inabout 60 cc of dry toluene was saturated with phosgene and then refluxeduntil all excess phosgene and hydrogen chloride were removed (about 5hours). Toluene was stripped off, the residue dissolved in about 20 ccof dry methylene chloride and a solution of5 g of bisphenol-A and 6 ccof dry pyridine in 50 cc of methylene chloride was added at once withstirring. Phosgene was now bubbled slowly into the stirred solutionwhich toward the end of the reaction turned moderately viscous. Theworkup and recovery of the product were carried out as described in theprevious example. A yield of 8 g of polymer was obtained which could becast into a clear rubbery film from chloroform solution. 3.Siloxane-carbamate/BPA-carbonate Copolymer, Si- Me /SiMeEtCN=3.3 Amixture of 25 g of octamethylcyclosiloxane (340 mmoles), 8.5 g ofcyanoethylmethylcyclosiloxane (mixture of trito hexasiloxane; 75 mmoles)and 5.4 g of l,3-bis(4-aminobutyl)-tetramethyldisiloxane (20 mmoles) washeated at 190 with about 10 mg of sodium hydroxide under nitrogen forhours. A solution of 20.5 g of the resulting homogeneous fluid (10.5mmoles) and 1.74 g of pyridine (22 mmoles) in about cc of methylenechloride (dried with phosphorous pentoxide) was added over a period of30 minutes to the stirred solution of 5.6 g ofbisphenol-A-bischlorocarbonate (15.9 mmoles) in 20 cc of dry methyleneHTABLEI 10 methylsiloxane order to quench the reaction and prevent gelformation. The solution was diluted with about two times the volume ofchloroform and washed three times with water. The product was recoveredby addition to metha- 5 no]. A yield of 23 g was obtained.

4. Siloxane-carbamate/BPA-carbonate Copolymer, Si- Me /SiMeEtCN=2.4

As described in the previous example, an amine-end stopped siloxanefluid was prepared from 22.4 g of dicyclic (300 mmoles), 11.3 gmethylcyanoethylsiloxane cyclic (100 mmoles), and

5.4 g of bisaminobutyldisiloxane (20 mmoles). As in Example 4, a portionof the product, 19.4 g, was reacted with 5.3 g of BPA-bischlorocarbonateand 1.65

15 g of pyridine and subsequently with 3.4 g of EPA, 5.0

g of pyridine and phosgene. The reaction product was precipitated byaddition to methanol containing about 20 percent of water. A yield of19.1 g of a tough, colorless rubber was obtained.

20 5. Siloxane-carbamate/BPA-carbonate Copolymer, Si-

. /iM9E A solution of 22.4 g of siloxane fluid prepared from 290 mmolesof methylcyanoethylsiloxane cyclic and 20 mmoles ofbisaminobutyldisiloxane was reacted with 25 6.1 g ofBPA-bischlorocarbonate and 1.91 g of pyridine, and subsequently with 3.9g of EPA, 5.8 g of pyridine and phosgene, as described in Example 3. Thepolymer was recovered by addition to methanol; a yield of 19.5 g oflight-tan-colored, tough rubber was obtained.

6. Siloxane-carbamate/BPA-carbonate Copolymer, Si- Me /SiMe(EtCN)=13 Anaminobutyl end-stopped siloxane fluid was prepared by heating 29.5 g ofoctamethylcyclotetrasiloxane (0.4 mole), 4.0 g ofcyanoethylmethylcyclosiloxane (0.035 mole), and 5.4 g of 1,3-bis(4-aminobutyl) tetramethyldisiloxane (0.02 mole) with about 10 mg of sodiumhydroxide at 190C for 15 hours under nitrogen. This fluid was reactedfirst with 3.24 g

0 of pyridine (0.041 mole) and 10.6 g of BPA-bischloro- Molar ratioMolar ratio (EPA/siloxane I l Weight (Me; S|/Me(EtCN)Si) segment) nnnsic percent Dielectric viscosity siloxane in Yield Starting StartingAnalysis (found/Cale) No. constant (2) 1. dl/g) copolymer (percent)Polymer material Polymer material C H N Si 1.8/1.6 23.8/222 g3 81 3.35.0 2.6 3 50.0/49.8 7.0/7.2 4.3/3.8 22.7l21.4 .171. .79 6; 2.4 3.0 2.753 50.6/50.5 7.0/7.1 5.9/4.3 21.6/20.7 5 ;:I 3 52 77 0.13 0.14 3.5 355.1/53.6 6.5/6.4 8.3/8.2 16.3/l6.5 42 2.2 3.2 9.3 5.7 53.5/54.9 6.4/6.63.7/3.2 18.7/17.0

Prepared with diisocyanato siloxane ll. Twice-precipitated product. 1nCHCL. 25.

chloride. tirring was c ontinued for another 30 min utes, then 3.6 g ofbisphenol-A (15.8 mmoles) and 5.3 g of pyridine (67 mmoles) was addedand a slow stream of phosgene was bubbled into the stirred solutionuntil a sharp rise in the viscosity indicated the end of the reaction.About l0 cc of methanol was quickly added in Examples6ttidtiuiifififiinc membranes made in accordance with our invention are asfollows:

EXAMPLE 1 A potassium ion-specific membrane was prepared by stirring 3.3mg. potassium tetraphenylborate with a slighTexcess of l2f2TrfgivETiiiBrn yEn iFYYnI. methylene chloride until all solids weredissolved. The time required was about three hours. Then 400.4 mg. ofsilo- I xane-carbamate/BPA-carbonate copolymer withdiisocyanatosiloxane, as described above under Prepa- 5 ration No. 2,was added to and dissolved in the methylene chloride solution. Thesolution was filtered, its volume reduced until it contained about 7percent polymer, and a film cast on a glass plate.

A potassium-ion specific electrode was formed by 10 punching out acircular portion of the composition film 0.23 inch in diameter to form apotassium ion-selective membrane and joining it to the end of a glasstube 0.20 inch in diameter with a silicone seal. The tube was filledwith an aqueous chloride solution of M1 mM sodium of 1.5 X 10 ohm'cm forthe membrane.

EXAMPLE 3 The above electrode of Example 1 was then life tested bystoring it in 100 mM potassium chloride solution. At various intervalsthe response and resistance have been measured over a period of 10.5months.

6 l After 7,600 hours no change in properties have been noted. The lifetest is continuing.

EXAMPLE 4 A membrane, which is Example 4, was prepared in the manner setforth above in Example 1 but was not made with a hydrophobic elastomericpolymer with a dielectric constant of from 4 to 13 or with a potassiumion-specific-membrane in accordance with the present invention. Anorganopolysiloxane polycarbonate block copolymer was selected which hada dielectric constant of 2.9, was hydrophobic and elastomeric. A H ioncarrier that is a hydrophobic, lipophilic uncoupler ofpoctadecyloxy-m-chlorophenylhydrazone mesoxalonitrile was employed.However, this membrane, when assembled and tested as described above inExamples 1 and 2 exhibited a resistance of l X 10 ohms and gave noresponse thereby showing its unsuitability as an ionspecific membrane.

While other modifications of the invention and variations thereof whichmay be employed within the scope of the invention have not beendescribed, the invention is intended to include such as may be embracedwithin the following claims:

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. A potassium ion-specific membrane which comprises a mixture of ahydrophobic elastomeric polymer of an organopolysiloxane polycarbonateblock copolymer with a dielectric constant of from 4 to 13, and apotassium ion-specific carrier selected from the group consisting ofnonactin, gramicidins, valinomycin, and mixtures thereof.

2. A potassium ion-specific membrane as in claim 1, in which thecopolymer is a carbamate-linked cyanoethylmethyl siloxane/bisphenol-Acarbonate copolymer. i k

2. A potassium ion-specific membrane as in claim 1, in which thecopolymer is a carbamate-linked cyanoethylmethyl siloxane/bisphenol-Acarbonate copolymer.